Euro PM2007 congress and exhibition

Abstract

Threatened with bureaucratic over-regulation under the EU's newly enacted REACH legislation, and other competitive challenges, the large tonnage section of the European PM industry did not seem to be facing a rosy future as it met in the Ville Rose city of Toulouse. Nevertheless, the EPMA was seen as having a key role in moving the industry forward and resisting the pressures from the large end users, low cost (Asian) producers, and competing technologies. Europe still leads the world in the manufacture of hard materials, but China is expected to overtake Europe in tungsten carbide and diamond tools production within the next 3–5 years. European sales of metal injection moulded parts continue to grow strongly, doubling in value to E140 million between 1997 and 2003. PM research in Europe is very active, with 40 universities and institutes and over 500 researchers involved. These provided the large majority of the European presentations at PM2007.     

Dissipative aspects in thermographic methods

Object of this paper is to emphasize some dissipative aspects of steels in high cycle fatigue from the thermographic point of view by relating anelastic and microplastic behaviours to loading levels respectively below and above the fatigue limit. To this aim, the Two Curves Thermographic Method has been modified by using both a parabola and a power curve as regression laws instead of the traditional linear ones. Two new thermal parameters have also been considered, the thermal increment and the subtended area by the thermal profile at a very low number of cycles. Experimental data referred to C45 standard and 25CrMo4 notched steel specimens have been processed using both original and modified Two Curves methodologies and both traditional and new thermographic parameters. All changes introduced in the present paper provide good results both in terms of fatigue limit values and for as concerns the rapidity of the fatigue tests.     

超高强度马氏体时效钢的研究与应用

介绍马氏体时效钢的种类,分析其强韧化机理,论述了典型的18Ni马氏体时效钢和无钴马氏体时效钢的化学成分和力学特性。系统阐述了循环相变热处理、形变热处理及等径弯曲通道变形(ECAP)这3种目前常用的细晶强化方法,并提出了马氏体时效钢的发展趋势及进一步深入研究强韧性和细晶强化的途径。     

Experience with the use of the acoustic emission technique for monitoring scale failure in wet and dry environments

Abstract

A brief survey of the acoustic emission technique for monitoring scale cracking and failure on 2.25–24% Cr steels in wet and dry environments is given. A number of acoustic emission test rigs are described. Some of the more simple test rigs are used for testing small oxidation coupons during isothermal oxidation. More sophisticated rigs have been used for testing full size heat exchanger tubes during thermal cycling.

Most acoustic emission measurements in a wet environment come from testing at temperatures below 650°C. There are examples from Alloy 800 and thermal barrier coatings that were tested at higher temperatures, 900°C and 1100°C, respectively. Through the years acoustic emission tests have been performed in dry air, dry air+10%H₂O, dry air+0.5%SO₂, and Ar+5%H₂+50%H₂O. Consequently, a wide variety of exposure temperatures and atmospheres can be investigated using acoustic emission techniques.

Qualitative acoustic emission results can detect when scale cracking occurs at exposure temperature, where such cracks are produced by growth stress. Acoustic emission signals have been measured during sample cooling, where the signal arises from scale cracking that is caused by the thermal expansion mismatch stress. Measured results have clearly shown that scale cracking caused by both growth stress and thermal expansion mismatch stress are affected by water vapor in the exposure environment. Post-test metallographic investigations show that crack orientation and the oxide scale phases are also affected by the gas composition in the test rig. Additionally the sample mass gain and scale thickness is affected by water vapor content.

Finally, acoustic emission techniques are helpful for understanding the phenomena of breakaway oxidation and spallation/exfoliation.     

Consideration of influence factors between small‐scale specimens and large components on the fatigue strength of thin‐plated block joints in shipbuilding

Shipbuilding in blocks, as being usual on all larger shipyards, requires that the blocks will finally be welded together manually or semi‐automatically, that is, with butt‐welds in transverse direction that have to withstand relatively high dynamical loads. Modern shipbuilding aims at lightweight construction with thin plates that may have a plate thickness down to 4 mm. Previous investigations showed that manually produced butt‐welds in such thin structures did not reach the calculated fatigue life as required in the rules. Up to the present, this problem has not yet been solved, and it is questioned if all influence factors on the fatigue behaviour of real structures are correctly considered as no damage cases at butt joints that are known yet. In the investigation described here, results from small‐scale specimens tested with cyclic loads will be transferred to large components, considering the effects of recorded pre‐deformations induced by welding as well as measured differences in residual stresses between small‐scale specimens and large components, thus clarifying how far for instance a detrimental stress ratio should be taken into account by the rules for thin plates.     

Experimental and theoretical formability analysis using strain and stress based forming limit diagram for advanced high strength steels

In this study, experimental and numerical analyses of Forming Limit Diagram (FLD) and Forming Limit Stress Diagram (FLSD) for two Advanced High Strength Steel (AHSS) sheets grade DP780 and TRIP780 were performed. Initially, the forming limit curves were experimentally determined by means of the Nakazima forming test. Subsequently, analytical calculations of both FLD and FLSD were carried out based on the Marciniak–Kuczinsky (M–K) model. Additionally, the FLSDs were calculated using the experimental FLD data for both investigated steels. Different yield criteria, namely, von Mises, Hill’s 48, and Barlat2000 (Yld2000-2d) were applied for describing plastic flow behavior of the AHS steels. Both Swift and modified Voce strain hardening laws were taken into account. Hereby, influences of the constitutive yield models on the numerically determined FLDs and FLSDs were studied regarding to those resulted from the experimental data. The obtained stress based forming limits were significantly affected by the yield criterion and hardening model. It was found that the forming limit curves calculated by the combination of the Yld2000-2d yield criterion and Swift hardening law were in better agreement with the experimental curves. Finally, hole expansion tests were conducted in order to verify the different failure criteria. It was shown that the stress based forming limit curves could more precisely describe the formability behavior of both high strength steel sheets than the strain based forming limit curves.     

Cyclic deformation and microstructural behaviour of reduced activation ferritic–martensitic steels

Abstract

The present paper presents results about cyclic behaviour and the evolution of the dislocation structure of reduced activation ferritic–martensitic steels and commercial martensitic steels AISI 410 and 420. The variation of the free dislocation density within subgrains and subgrain size was mainly analysed during the cyclic softening of EUROFER 97 steel. From the analysis of the flow stress components, the friction and back stresses, and the information of the evolution of the dislocation structure, it could be concluded that the softening of tempered martensitic steels at 20°C is produced by the contribution of the friction stress and aided later by the back stress.     

Corrosion of aluminium,stainless steels and AISI 680 nickel alloy in nitrogen‐based fuels

Nitrogen‐based compounds can potentially be used as alternative non‐carbon or low‐carbon fuels. Nevertheless, the corrosion of construction materials at high temperatures and pressures in the presence of such fuel has not been reported yet. This work is focused on the corrosion of AISI Al 6061, 1005 carbon steel (CS), 304, 316L, 310 austenitic stainless steels (SS) and 680 nickel alloy in highly concentrated water solution of ammonium nitrate and urea (ANU). The corrosion at 50 °C and ambient pressure and at 350 °C and 20 bar was investigated to simulate storage and working conditions. Sodium chloride was added to the fuel (0–5 wt%) to simulate industrial fertilizers and accelerated corrosion environment. Heavy corrosion of CS was observed in ANU solution at 50 °C, while Al 6061, 304 and 316L SS showed high resistance both to uniform and pitting corrosion in ANU containing 1% of sodium chloride. Addition of 5% sodium chloride caused pitting of Al 6061 but had no influence on the corrosion of SS. Tests in ANU at 350 °C and 20 bar showed pitting on SS 304 and 316L and 680 nickel alloy. The highest corrosion resistance was found for SS 310 due to formation of stable oxide film on its surface.     

双回路直线型钢管角钢输电塔静动力分析

采用有限元分析软件ANSYS对500 kV双回路直线型圆管角钢输电塔进行了静动力分析,研究方法及主要结论如下：运用静风极限承载力的分析方法,计算出铁塔在各个方向的极限承载力较为接近,通过塔体动力特性的分析,变刚度处设计应予以重视。